1. Field of the Invention
The present invention relates to an image processing apparatus which is suitable for use in, for example, a facsimile apparatus, an electronic filing apparatus, an image reader, a digital copier, or the like.
2. Description of the Prior Art
According to a conventional method of binarized gradation processing an image by way of a dither method, the image signal read out is directly compared as an analog signal with a dither threshold value or after it has been converted to the digital signal, this digital signal is compared with the dither threshold value and, in this case, the dither threshold value is two-dimensionally changed in correspondence to the division of the read image.
FIG. 1 is a diagram showing a concept of binarization by way of a dither method. The image signal is compared with the dither threshold value stored in a memory 101 such as a ROM or the like by a comparator 100. For example, a white signal is outputted when the image signal is higher than the dither threshold value, while a black signal is outputted in the opposite case. The values shown in the memory 101 represent the dither threshold values.
By use of this method, the image of a photograph or the image of continuous gradations of a half-tone can be reproduced as a beautiful gradation image. On the contrary, however, there is a drawback that the resolution deteriorates since pattern images such as characters, diagrams, or the like are also subjected to gradation processing.